What's more, people who took part in the commercial diet plan had better blood sugar control after a year.
"I think this should be a huge ray of hope for people that lifestyle changes are possible and there are some things that don't cost an arm and a leg," Cheryl Rock told Reuters Health. She is the study's lead author from the University of California, San Diego.
Jenny Craig, the diet program used in the new study, funded the research and consulted with researchers during the development of the study. The company had no part in the collection, analysis and publication of the data in the journal Diabetes Care.
Over one-third of U.S. adults are obese, according to the Centers for Disease Control and Prevention. Obesity is linked to a number of health conditions, including heart disease, stroke and type 2 diabetes.
Type 2 diabetes, sometimes referred to as adult-onset diabetes, is when the body's cells are resistant to insulin or the body doesn't make enough of the hormone, so glucose remains in the bloodstream and can climb to dangerously high levels. Insulin gives glucose - or blood sugar - access to the body's cells to be used as fuel.
Past research has found that lifestyle interventions, including diet and exercise, can help people better manage their blood sugar and control risk factors for heart disease, write the researchers.
The Jenny Craig plan had been found to help people lose about 8 percent of their body weight after two years in a previous study. The plan had not been tested among people with type 2 diabetes, however.
The researchers recruited 227 overweight and obese adults with type 2 diabetes and randomly assigned them to one of three groups.
One group of 76 received so-called usual care, which consisted of two weight loss counseling sessions and monthly checkups.
A group of 74 was put on a lower-fat Jenny Craig diet, and another group of 77 received a lower-carbohydrate Jenny Craig diet.
People in the commercial weight loss groups received packaged meals, a menu plan and frequent one-on-one counseling sessions - all provided free by Jenny Craig. They were also encouraged to increase their physical activity.
After one year of the study, 38 percent of participants in the commercial weight loss groups had lost at least 10 percent of their initial weight. That compared to about 9 percent of those receiving usual care.
In addition, 72 percent of participants in the commercial weight loss groups who needed to inject insulin before meals at the start of the study had stopped taking their insulin or cut back on the amount they used. That compared to 8 percent in the usual care group.
As for differences between the two commercial weight loss groups, the researchers found that those in the lower-carbohydrate group appeared to have better blood sugar control during the last three months of the study, compared to the lower-fat group.
Rock said it may not be one specific aspect of the Jenny Craig diet that led to the better results. It may be a combination of factors, including the structure and social support.
Previous studies have found commercial weight loss programs, including Weight Watchers, to be effective.
Dr. Merle Myerson, a cardiologist who was not involved with the new study, said people on the commercial weight loss program saw great results, but "I don't think it tells us anything great or new."
Myerson is director of the Cardiovascular Disease Prevention Program at Mount Sinai St. Luke's and Mount Sinai Roosevelt hospitals in New York.
"I would have liked to see what happens in two years," she said, such as whether people stay with the program and sustain their weight loss.
"It can work, but I think it's a stretch to generalize and say this would definitely be an option, because we only have one year of results," Myerson added.
The program offered in the new study, known as Jenny Craig for Type 2, costs $29 per month. That does not include the $15 to $22 per day of prepackaged meals and shipping costs.